Acoustic cap for stacks



Dec. 2, 1958 R. B. JACOBS ET A1. 2,862,570

ACOUSTIC CAP FOR STACKS Filed June 29, 1955 v 2 Sheets-Sheet 1 Dec- 2, 1958 R. B. JACOBS ET'AL 2,862,570

ACOUSTIC CAP FOR STACKS T o s; ai is pitted.

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acorisric can sracirs Robert E. .lacobg Homewood, and Erwin Ginsburgh, Chicago, iii., assignors to Standard @il Company, Chicago,

This invention relates to reducing noise on stacks and, more particularly, is concerned with an apparatus for reducing noise when exhausting high pressure gases which contain erosive solids suspended therein.

in many modern petroleum refineries it is desired to conduct operations wherein exhaust gases are vented from high pressure chambers wherein the vented gases have contacted a bed of fluidized finely divided solids. Solids from such operations remain entrained in the exhaust gases and these solids erode stack silencers heretofore available with the result that frequent and costly repairs are necessary. Many types of silencers have been designed and attempted for use on this difficult duty but heretofore none has been satisfactory from the standpoints of noise attenuation, erosion resistance, and ease of replaceability when necessary.

It is, therefore, an important object of our invention to provide a stack silencer which is of rugged and simple construction making for easy fabrication and replacement. An additional object of our invention is to provide an apparatus which is particularly effective on the venting of gases containing finely divided or entrained solids. A fun ther object is to provide an apparatus which is effective in noise attenuation over a wide range of frequencies. Still another object of our invention is to provide an effective stack silencer which is not affected by erosion.

Although the invention is primarily directed toward the solution of a serious problem in connection with the venting of gases from petroieum refining equipment, an object of the invention is to provide a vtype of staclc silencer which will be generally useful for controlling the flow of fluids and reducing the noise thereof, particularly when said fluids contain erosive solids. A more specific object of the invention is to provide a method and means for reducing or eliminating the noise of flue gases from a catalyst regenerator outlet pipe. These and other objects of our invention will become apparent as. our description thereof proceeds.

Briefly, we attain the objects of our invention by providing an acoustic cap which comprises a sleeve which is mounted about the upper end of a stack and spaced there from to provide an annular chamber, the lower' end of the annular chamber being closed by a bottom closure plate. A plurality of gas ports in the portion of the wall of the stack enclosed by the sleeve discharge into the annular chamber. Across the fiow area of the stack above the ports, we provide a cap plate which supports a perforated support containing a quantity of sound-absorbing refractory fiber. This produces a cylindrical chamber closed at its upper end. The height of such chamber above the ports and below the cap is such that the travel of any finely divided solids entrained by the stack gases will be spent and the solids will fall back or settle within the quiescent fallout chamber at the closed upper end of the stack. The separated or settling solids are resuspended in a subsequent flow of gases which issue laterally from the ports and then upwardly within the annular chamber. This results in a minimum of erosion due to iinpingement A be streamlined to prevent generation of sound during the venting of the gases from the stack through the lateral ports.

To illustrate our invention, we will describe embodiments thereof which may be applied to stacks on fluidized catalyst systems. ln the operation of fluid catalyst processes, it may be necessary to regenerate or otherwise treat the catalyst in a large body by blowing gases therethrough and venting the gases to the atmosphere. Because of the tine state of subdivision of the catalyst, considerable quantities of the catalyst may be carried from the contacting chamber with the waste gases. Because of the large volume of gases, it has been a difficult problem to devise a throttling means which will effectively reduce the pressure from the contacting pressure to the pressure of the atmosphere without generation of objectionable noise and without serious erosion of the equipment.

Various types of throttling valves have been tried for the purpose and, although it is possible to throttle the gases to atmospheric pressure with a tolerable erosion of the throttling valves by the entrained solids, the design of such throttling valves have inherently generated excessive sound. However, our acoustic cap construction makes possible the use of such throttling valves within the stack and permits the venting of the stack gases to the atmosphere without attaining the objectionable level of noise customarily associated with such venting.

Further details of the construction and advantages of our atmospheric cap will be described in connection with preferred embodiments thereof which are illustrated in the drawings and wherein:

Figure l is an elevation of our cap, partly in section; Figure 2 is a section taken along the line 2-2 in Figure Figure 3 illustrates a modification of the cap shown in Figure l; and l Figure 4 is a section taken along the line in Figure 3.

Referring to the drawings, the stack lo, provided with the conventional refractory lining ll, is provided with ports l2 in the wall of the stack l@ at the upper end lfia thereof. At vertically spaced points in the stack lil we provide conventional fixed orifice throttle plates which, since they do not form a part of the present invention, are not shown in the drawings. However, many such throttle plates or valves are available for this duty and can readily be supplied by those skilled in the art. These are all characterized, however, by generating sound which we reduce by means of our acoustic cap.

The member itin, which if desired may comprise a separate cylindrical extension of the stack lo, is closed at its upper end 'by a circular plate i3 and supported therein, for example, by cross members or beams ld. A perforated support 15 is held to plate by bolts i6, the support i5 confining mass i7 of sound-absorbing refractory fiber such as glass cr asbestos wool.

An outer housing or sleeve i3, supported on annular bottom closure plate i9, surrounds the cylindrical member lila and forms the annular chamber 20 which is provided with sound-absorbing*lining 2l on both walls. A

fire-brick floor Z2, or `other sound absorber is provided in the base of the annular chamber 2'@ to `absorb further sound which comes through the .ports l2. A safety screen 23, supported on frame-work Z4, is carried by the top of Jthe unit to retain large objects which might otherwise be ejected from the stack.

ln operation, the flue or stack gases with entrained solids tlow upwardly within stack l@ generating entrained sound in passing through the throttle Zones. On reaching the ports l2, the solids tend to continue upwardly beyond them and their erosive energy is spent within the quiescent fall-out or settling zone 25. The pad 17 is placed a distance of at least 3 feet above the ports l2 with a ow rate of exhaust gases of less than about lili) feet per second. The gases pass through the ports l2 into annular sound-absorbing chamber Ztl, and the entrained sound is absorbed by the pad 17 in the top of the solidsseparating zone 25. ln so doing, finely divided solids, which fall downwardly within the zone 2S', are resuspended in a subsequent flow of gas and carried through the ports l2. The sound-absorbing and abrasion-resistant lining 2l on the concentric walls of the chamber Ztl minimize and reduce noise generated in the throttle Zones and not absorbed by the sound-absorbing .pad l?, or noise generated by the ilow of gases through the ports l2 `will be absorbed by the lining 2l. before discharge to the atmosphere.

In Figures 3 and 4, further design modications are illustrated for reducing the entrained sound which reaches the annular chamber Ztl. This may be accomplished by providing a plurality of radially-extending partitions 2d. Each partition comprises a pair of perforated plates 27 and 2@ with a sound-absorbing layer 2? therebetween. The bottom of the annular space conned by the adjacent pairs of partitions 26 is tilled with a refractory cement 3l and formed in a `streamlined fashion so as to reduce to a minimum the generation of noise by the gases in issuing from the ports l2. Further, the flow area of the ports 12 and of the streamlined sound-absorbing charn- 'bers 30 is designed to 'be at least equal to the flow area in section lila. i

The blanked--off portion 38 of the annular chamber 3@ between adjacent ports l2 may be provided with reenforcing or support plates 39 which extend `between the inner cylinder lila and the outer cylinder lll. A number of top cover plates llt) complete the enclosure of the blanked-oif Isection 38. These are removable so that the sound-absorbing :material 29 (whether it be such as -rebrick `or special cement) can be readily replaced.

`ln a typical installation, the stack may have an internal diameter of about feet with an abrasion-resistant refractory cement lining 2l about 1.5 inches thick. The `sound-absorbing pad 17 is at least about 6 feet above the upperedges of the ports l2, each port l2 representing an opening about 21 inches wide and about 3 feet, 4.5 inches high. The top and side edges of the ports l2 may be re-enforced by cut sections 33 of 3-inch pipe t-o provide a streamlined opening l2.

The silencer or sound-absorbing sleeve lltl may suitably have an internal diameter of about 8 feet, 8 inches providing, after application of 1.5 inch thick linings 2l, an annular chamber 3@ between member lilo and sleeve lll which is about 'inches wide. Acess to the soundabsorbing chamber 34) may be had through the sleeve lid by means of removable plate Ell and secured thereto by conventional means.

The sound-absorbing pad ll? may comprise about 6 inches of refractory ber confined between the plate l and the support l5, the support l5 being made in quarter sections and perforated with l@ inch holes o-n inch staggered centers. Stainless steel bolts lr6 secure the basket sections to the plate lll.

The entire unit can be supported at the top of the stack l@ by means of support beams 35 extending between the plate 19 and the re-enforcing ring 36 about the stack, The internal lining lll within section )lila is retained by the ring 32, there being no necessity for the abrasion-resistant. lining llll in the top section of the member ltlcz, which shown in the drawings is integral with the stack lil. Howl ever, it may be desirable to re-enforce the lining 2l on the outer wall of member lele; and we may provide plates 37 fixed to the shell and extending radially beyond the lining 2l for such purpose.

installations such as that described above have proven very satisfactory in service and have solved an otherwise difficult and bothersome noise problem in renery areas. In any event from t' e above it will be apparent that we have devised an acoustic cap which absorbs the entrained sound produced by the throttling valves within a lower portion of stack Likewise, by the positioning of the sound-absorbing pad l? at a point substantially above the vent ports l2, we have for all practical purposes eliminated the erosive effect of the entrained solids within the cap.

Although we have described our invention interms of a single unit at the top of a stack, it is also contemplated that we may arrange a plurality thereof in superposed series. For such purposes, additional ports l2 are provided on the inner wall of the annular chamber Ztl to discharge above tte cap plate E3 into an extension of the member lita. Also, an annular sound-absorbing pad, similar to should be provided at the top of the annular space Ztl. This modified series arrangement can be repeated as necessary to multiply the effect of the single silencer illustrated in the drawings.

Modifications in the structure and in the mode of operation of the apparatus described herein can be made by those skilled in the art without departing from the invention, and it should be understood that the embodiments described in some detail and shown in the drawings are for the purpose of illustrating the invention without being limited thereto.

What we claim is:

l. An acoustic cap .for reducing stack noises generated by venting line gases containing finely divided solids which comprises in combination a sleeve arranged about the upper end of a stack and spaced therefrom to provide an annular chamber, plate means for closing the lower end of the annular chamber between said stack and said sleeve, means for supporting said bottom closure plate means and said sleeve on said stack, a plurality of flue gas ports in the wall of said stack and discharging therefrom into said annular chamber, a cap plate assembly across the upper en'd of said stack, said assembly ineluding a cap plate, a perforated support fixed below said cap plate, and a quantity of sound absorbing fiber disposed between said perforated support and said cap plate, linings within said sleeve and on the outer surface of said stack comprising abrasive-resistant refractory sound-absorbing means, the distance between said ports in said stack and the stack cap plate assembly with its sound-absorbing fiber being suticiently great so that entrained solids cannot impinge at their flow velocity on said cap plate assembly, a plurality of pairs of perforated spaced metal plates partitioning the said annular chamber, Iand an acoustic absorber means between adjacent plates in said pairs, the sub-chambers of the said annular chamber so produced being stream-lined with respect to the ilow of flue gases from said ports.

2. The structure of claim t wherein the total ow area of the ports is at least equivalent to the flow area of said upper end of said stack and wherein said cap plate assembly is placed a distance above said ports of at least 3 feet with a flow rate of' exhaust gases into said upper end of said stack. of less than about feet per second.

3. An acoustic absorber cap for reducing stack noise and enhancing separation of suspended solids with a minimum of erosion which comprises in combination a rst tubular member of substantially the diameter of the stack on which it is applied, an acoustic absorber plate means across the upper end of said tubular member, several large vent ports in the wall of member adjacent only the end thereof remo-te from said plate, the area of said ports being at least equal to the flow area of the said first tubular member, an annular bottom closure extending radially from the outer wall of said tubular member ata point below said ports, a second tubular member spaced from said irst tubular member and supported by said bottom closure to provide an annular chamber surrounding said tubular member, vent means from said annular chamber disposed at a level above said acoustic absorber plate means and through which line gases iiow from said ports into the atmosphere, and a sound-absorbing lining on the walls and oor of said annular chamber, the annular chamber being divided into a plurality of streamlined, sound-absorbing channels, each such channel communicating with only one of said ports and being of substan.

tially the same cross-sectional ow area as that of each port.

4. The acoustic cap of claim 3 wherein the acoustic absorber plate means includes a perforated support means, a mass of sound-absorbing refractory fiber within said support means, the distance between the ports and said sound-absorbing mass being greater than the distance of travel of the entrained solids which separate from the gases venting through the said ports whereby there is a minimum of impingement of said sound-absorbing plate means by the said solids.

5. An acoustic cap for reducing stack noise wherein uids containing finally divided solids are vented which comprises an annular plate means disposed about a stack, a cylindrical casing supported by said annular plate means and arranged concentric to the stack to provide an annular chamber, a cap plate means disposed across an upper portion of said stack thereby providing a sound-attenuating and solids-separating chamber at the top of said stack, several large ow ports in the wall of said stack discharging into said annular chamber, vent means from said annular chamber discharging at a level above said cap plate means, and sound-absorbing linings within said annular chamber and within said stack, said annular chamber being divided into a plurality of streamlined channels, each communicating with only one of said ports thereby to minimize the level of noise resulting from the venting of the gases through said ports, whereby noise generated within said stack below said cap is substantially absorbed by said absorbing cap plate means and whereby entrained solids are separated from the owing gases Within the said sound-attenuating and solids-separating chamber at the top of said stack.

References Cited in the file of this patent UNITED STATES PATENTS 282,933 Shoptaugh Aug. 7, 1883 711,338 Naef Oct. 14, 1902 763,626 Ogden June 28, 1904 1,665,754 Pritchard Apr. 10, 1928 1,927,213 Mackenzie et al Sept. 19, 1933 1,990,837 Morgenstern Feb. 12, 1935 2,065,343 Moore et al Dec. 22, 1936 2,600,262 Powers June 10, 1952 2,640,557 Gaifney June 2, 1953 

